1. Field of Invention
The present invention relates generally to the design and fabrication of flush inlets for marine or aeronautical applications and, more particularly, to a hydrodynamically designed, integrated inlet duct having a short length and a steep duct inclination angle and which provides efficient and cavitation free transmission of a fluid therethrough.
2. Brief Description of Related Art
Flush inlets have been used in both nautical and aeronautical applications. Nautical applications have included inlets for water jet propulsion systems for high speed marine vehicles. Aeronautical applications have included air inlet for engines of high speed aircraft.
Theoretically, the optimum inlet should be designed to match the flow at the vehicle design speed and power. At this condition, the inlet has the optimum inlet velocity ratio and is entirely free from cavitation. Strictly, all other conditions require a different inlet area to maintain the optimum inlet velocity ratio and energy recovery. Past water jet propulsion systems have attempted to provide improved propulsive and cavitation performance over wider speed ranges by using such devices as variable geometry inlets. However, these mechanically complicated schemes add weight and cost to the system.
The design of an optimum inlet for a given application should include model testing and iterative adjustments of geometry guided by the designer's experience and theoretical knowledge. However, this is economical only in large projects. Usually, except in very large projects, a standard inlet geometry, which has been found to give acceptable performance, is used. If designed for a particular application, prior art inlets have optimum efficiency at a particular design condition (i.e., a particular design speed and power). However, efficiency drops off rapidly at off design conditions. The inlet geometry, if optimized at all, is designed to match the flow at the vehicle design condition. Consequently, flush or semi-flush inlets have generally had ramp-angles (duct inclination angles) that are less than about 30.degree. relative to a substantially horizontal inlet plane. These shallow-ramp-angle inlets generally include a long radius of curvature leading edge lip (upstream transition from hull surface to inlet duct) resulting in duct lengths, from inlet to pump impeller, that are quite long. Consequently, viscous losses in the duct are high. Furthermore, at low ship speeds, flow separation at the inlet may occur due to pump suction induced flow angles that are high relative to the shallow-ramp-angle.
A further disadvantage of present inlet designs is the method of designing and locating the inlet with respect to the body in which the inlet is mounted. Inlet ducts operate under very complex three-dimensional flow conditions. Consequently, efficiency and cavitation performance of water jets is very dependent on a good design of the water inlet. However, prior inlet design methods have been restricted to considering simple two-dimensional momentum theory and two-dimensional flow regimes. As a result, the design and locating of water jet inlets has been generally confined to considering symmetric flow. Moreover, present inlet design methods have not provided a method in which design modifications can be readily accomplished within an iterative design process.
Consequently, there is a need for an iterative inlet design method that offers a simple means of modifying the inlet design and evaluating the effects of the modifications within the iterative process. There is a further need for a simple design method that produces an inlet duct design having high efficiency and good cavitation performance at both low speeds and high speeds. There is a further need for a system that offers flexibility of placement while minimizing the various losses associated with the inlet.